Current detection apparatus

ABSTRACT

A current detection apparatus includes two magnetic detectors that are arranged oppositely on a front surface and a back surface of a board which is located above a current path in order to detect a strength of a magnetic field, an electromagnetic shielding frame member that is mounted on the current path so that the two magnetic detectors and a part of the current path are accommodated inside the electromagnetic shielding frame member, and a control circuit that determines whether a failure which occurs in either of the two magnetic detectors from a difference between magnetic fields detected by the two magnetic detectors, respectively. Sensitivities of the two magnetic detectors are made adjusted so that current values outputted from the two magnetic detectors depending on detected magnetic fields are identical to each other in a normal state.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/637,841, filed Sep. 27, 2012, which is a national phase ofinternational application No. PCT/JP2011/060369, filed Apr. 28, 2011,which claims priority from Japanese Patent Application No. 2010-104291filed Apr. 28, 2010, the entire subject matters of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a current detection apparatus whichuses a magnetic detector which is provided near a current path in anelectronic equipment of a car such as a motor to detect a value of acurrent which flows in the current path, and particularly to a currentdetection apparatus which can detect a failure which occurs in themagnetic detector.

BACKGROUND ART

In order to detect a current which flows in a current path (for example,in a bus bar) which connects an in-vehicle battery of a vehicle andelectronic equipments of the vehicle, a current detection apparatus isused. For example, as shown in Patent Literature 1, the currentdetection apparatus includes a core of a ring shape, a magnetic gapwhich is formed by opening a part of the core, and a Hall element whichis arranged in the magnetic gap, and is configured so that the value ofa current which flows in the current path which is inserted into thecore of a ring shape is detected by the Hall element which is arrangedin the magnetic gap.

Therefore, in the current detection apparatus, when a magnetic field isgenerated in the core of the ring shape by the current which flows inthe current path, the Hall element in the magnetic gap generates avoltage (Hall voltage) due to Hall Effect in accordance with themagnetic field. At this time, the core functions to strengthen themagnetic field generated by the current which flows in the current path.Since the Hall voltage which the Hall element generates corresponds tothe magnetic field strength in the core and corresponds to the value ofthe current which flows in the current path which generates the magneticfield, the current value can be detected.

In such current detection apparatus, in order to obtain a detectioncurrent in a sufficient level so that current detection performance maynot be dropped, two Hall elements are provided in the magnetic gap ofthe core. Thereby, compared with the case of one Hall element, a currentin almost two times levels can be detected. The two Hall elements arejuxtaposed in the thickness direction of the core or the direction ofmagnetic force lines which pass the magnetic gap.

Thus, in the related-art current detection apparatus, a current in adesired level can be detected by providing two Hall elements in themagnetic gap of the core.

CITATION LIST Patent Literatures

Patent Literature 1: JP-A-2007-155400

Patent Literature 2: Japanese Patent Application No. 2008-306360

SUMMARY OF INVENTION Technical Problem

However, in the related-art current detection apparatus, since the coreof the ring shape in which the two Hall elements are provided in themagnetic gap is required, there is an inconvenience that the size of thewhole device becomes large, and there is also an inconvenience with arestriction of a mounting structure of the core with respect to thecurrent path due to the fact that the current path is put inside thecore. Although the current detection apparatus disclosed in PatentLiterature 2 makes the core of a ring shape unnecessary, two magneticdetectors must be arranged on the same plane, which also becomesdisadvantageous for the downsizing of the whole device in this case.Patent Literature 2 is disclosed on Jun. 10, 2010 as JP-A-2010-127896.

The present invention is made in view of the situation mentioned above,and an object of the invention is to provide a current detectionapparatus which enables the downsizing of the apparatus, and which canperform failure determination of Hall elements with high precisionwithout being affected by an external magnetic field.

Solution to Problem

The above object of the invention is achieved by the followingconfiguration.

(1) A current detection apparatus, including:

two magnetic detectors that are arranged oppositely on a front surfaceand a back surface of a board which is located above a current path inorder to detect a strength of a magnetic field which is generated by acurrent which flows in the current path;

an electromagnetic shielding frame member that is mounted on the currentpath so that the two magnetic detectors and a part of the current pathwhere the two magnetic detectors are arranged are accommodated insidethe electromagnetic shielding frame member; and

a control circuit that determines whether a failure which occurs ineither of the two magnetic detectors from a difference between magneticfields detected by the two magnetic detectors, respectively, wherein

sensitivities of the two magnetic detectors are adjusted so that currentvalues outputted from the two magnetic detectors depending on detectedmagnetic fields are identical to each other in a normal state.

According to the current detection apparatus, since it is not necessaryto include the core in structure like before and at least only onemagnetic detector should be arranged at the same plane, thesimplification and downsizing of the current detection apparatus arepossible, and failure determination of the magnetic detectors (Hallelements) can be easily performed without being affected by an externalmagnetic field.

(2) The current detection apparatus according to the configuration (1),wherein each of the two magnetic detectors is arranged to be located ata center of the current path in its widthwise direction.

According to the current detection apparatus, since the magneticdetectors are arranged at parts where the magnetic field strengthgenerated from the current path becomes the largest easily, the size ofthe current which flows through the current path can be measured withsufficient precision.

Advantageous Effects of Invention

According to the current detection apparatus of the invention, since itis not necessary to include the core in structure like before and onlyat least one magnetic detector should be arranged at the same plane, thesimplification and downsizing of the current detection apparatus arepossible, and failure determination of the magnetic detectors (Hallelements) can be easily performed without being affected by an externalmagnetic field.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a current detection apparatus according to thepresent invention.

FIG. 2 is a top view of the current detection apparatus shown in FIG. 1.

FIG. 3 is a sectional view of the current detection apparatus takenalong a line indicated by III-III shown in FIG. 2.

FIG. 4 is a top view for conceptually describing the installed positionof a magnetic detector which forms a Hall IC shown in FIG. 2 inside anelectromagnetic shielding frame member.

FIG. 5 is a sectional view inside the electromagnetic shielding framemember taken along a line indicated by V-V shown in FIG. 4.

FIG. 6 is an explanatory view which shows the distribution of magneticflux Bw in a widthwise direction of a bus bar which a current pathgenerates in the electromagnetic shielding frame member.

FIG. 7 is an explanatory view which shows the distribution of magneticflux Bl in a longitudinal direction of the bus bar which a current pathgenerates in the electromagnetic shielding frame member.

FIG. 8 is a block diagram which shows a failure detecting circuit of thecurrent detection apparatus.

FIG. 9 is a graph which indicates a correlation of the distance in the Ydirection from the Y center position with magnetic flux density.

FIG. 10 is a graph which shows failure detection regions when two HallICs whose sensitivities can be adjusted are used.

MODES FOR CARRYING OUT INVENTION

Next, a preferred embodiment of the current detection apparatusaccording to the invention is described with reference to the figures.In the embodiment, a Hall IC is adopted as a magnetic detector whichdetects the strength of a magnetic field generated by a current whichflows through a current path.

FIG. 1 is a side view of the current detection apparatus according tothe present invention. FIG. 2 is a top view of the current detectionapparatus shown in FIG. 1. FIG. 3 is a sectional view of the currentdetection apparatus taken along a line indicated by III-III shown inFIG. 2. FIG. 4 is a top view for conceptually describing the installedposition of a magnetic detector which forms a Hall IC shown in FIG. 2inside an electromagnetic shielding frame member. FIG. 5 is a sectionalview inside the electromagnetic shielding frame member taken along aline indicated by V-V shown in FIG. 4. FIG. 6 is an explanatory viewwhich shows the distribution of magnetic flux Bw in a widthwisedirection of a bus bar which a current path generates in theelectromagnetic shielding frame member. FIG. 7 is an explanatory viewwhich shows the distribution of magnetic flux in a longitudinaldirection of the bus bar which a current path generates in theelectromagnetic shielding frame member. FIG. 8 is a block diagram whichshows a failure detecting circuit of the current detection apparatus.FIG. 9 is a graph which indicates a correlation of the distance in the Ydirection from the Y center position with magnetic flux density. FIG. 10is a graph which shows failure detection regions when two Hall ICs whosesensitivities can be adjusted are used.

The current detection apparatus of the embodiment includes a base block12 and a terminal block 13 as housing which forms an external shape ofthe current detection apparatus, an electromagnetic shielding framemember 14 which covers the side surfaces of the base block 12 and theterminal block 13, and two Hall ICs 15, 16 which are attached onto theterminal block 13. The base block 12 is a housing which is located belowa bus bar 11 (lower side in FIGS. 1 and 3), and is fixed to the bus bar11. On the other hand, the terminal block 13 is a housing which islocated above the bus bar 11, and is fixed when being placed on the baseblock 12. The electromagnetic shielding frame member 14 is mounted onthe bus bar 11 so that the two Hall ICs 15, 16 and a part of the bus bar11 which is arranged near the Hall ICs 15, 16 are contained inside.

If a current flows in the bus bar 11, a magnetic field will occur aroundthe bus bar 11. The magnetic field is detected by each of Hall elements(magnetism detecting elements) in the Hall ICs 15, 16 which areinstalled on the terminal block 13, and a voltage which each of the Hallelements detects is amplified by an amplifying circuit in each of theHall ICs 15, 16, and a voltage value which is proportional to thedetected magnetic field is output. That is, based on the output from theHall element, the detection of the value of a current which flows in thebus bar 11 is performed.

The base block 12 is molded of insulating material, such as plastic, anda fitting notch (concave groove) 17 which accommodates a specifiedlength of the bus bar 11 and fits to the bus bar 11 is formed on the topsurface of the base block 12. Threaded holes 18 which are penetratedthrough from top to bottom are provided near both ends in the lengthdirection (X direction shown in FIG. 2) of the base block 12. Thesethreaded holes 18 are used to screw the bus bar 11 tightly onto the baseblock 12. A fitting notch (concave groove) 19 for the electromagneticshielding frame member 14, which covers the side surfaces (side surfacesin the Y direction) of the base block 12 and the terminal block 13 for aspecified width in the length direction (X direction) and the bottomsurface of the base block 12, is formed on the bottom surface of thebase block 12. When the electromagnetic shielding frame member 14 ismounted on the base block 12 and the terminal block 13, theelectromagnetic shielding frame member 14 is accommodated in the fittingnotch (concave groove) 19.

The bus bar 11 is a conductive plate whose widthwise (Y direction)dimension is constant, and mounting holes 20 are provided to bepenetrated at parts corresponding to the threaded holes 18 formed in thebase block 12. Therefore, by installing the bus bar 11 to the fittingnotch 17 on the base block 12, and screwing stop screws 12 a into thethreaded holes 18 through the mounting holes 20 from the top surface ofthe bus bar 11, the bus bar 11 can be strongly attached to the baseblock 12. Thereby, the bus bar 11 is stably supported by the base block12.

The terminal block 13 is molded of insulating plastic material, and isplaced on the base block 12. The terminal block 13 has integrally an ICreceiving recess 21 for receiving Hall ICs and a connector insertioncylinder 22 for accommodating a mating connector (not shown in thefigures). An insulative board 23 is fixed to the IC receiving recess 21,and the two Hall ICs 15, 16 and conductive circuit patterns (not shownin the figures) are arranged on the front and back surfaces 23 a and 23b of the insulative board 23. Each of the Hall ICs 15, 16 are a chipwhich integrates a Hall element and an amplifying circuit as a magneticdetector, and an analog type chip which outputs a voltage proportionalto the detected magnetic field strength is used. The amplifying circuitamplifies the voltage output, and converts the voltage output to acurrent value and outputs the result. The arrangement parts of the HallICs 15, 16 to the IC receiving recess 21 are described later.

On the other hand, one end of each of a plurality of connector pins 24is protruded from the bottom of the connector insertion cylinder 22, andthe other end of each of these connector pins 24 is embedded in theterminal block 13. The other ends of the connector pins 24 which areembedded in the terminal block 13 are connected to the connectionterminals of the Hall ICs 15, 16 via leads 25 which are embedded in theinsulative board 23. When a female connector (not shown in the figures)is fitted in the connector insertion cylinder 22, and connecterterminals at the side of the female connector are inserted into theconnector pins 24, the output signals of the Hall ICs 15, 16 can beextracted to an external circuit.

The electromagnetic shielding frame member 14 is formed in a U shape sothat the side surfaces of the base block 12 and the terminal block 13(especially those portions that faces the side surfaces of the ICreceiving recess 21 which accommodates the Hall ICs 15, 16 among theside surfaces of the base block 12 and the terminal block 13) arecovered, and is fitted into the fitting notch 19 of the base block 12 asmentioned above. In the electromagnetic shielding frame member 14, crimpclaws 26 which are protruded in the height direction (Z axial direction)are formed at ends of the parts where the side surfaces of the baseblock 12 and the terminal block 13 are covered, and the crimp claws 26are crimped and attached to upper opening edges 21 a of the IC receivingrecess 21. When the bus bar 11 and the base block 12 which is attachedto the bus bar 11 are received inside the U shape, by crimping andattaching the crimp claws 26 of the electromagnetic shielding framemember 14 to the upper opening edges 21 a of the IC receiving recess 21,the terminal block 13 placed above the base block 12 is firmly held onthe base block 12. Therefore, the bus bar 11 is also definitely heldbetween the blocks 12 and 13. Electromagnetic waves can be preventedfrom being propagated from the outside of the IC receiving recess 21 tothe inside of the IC receiving recess 21 when the electromagneticshielding frame member 14 covers the side surfaces of the IC receivingrecess 21.

The long bus bar 11 is inserted into the fitting notch 17 formed in thecentral part of the base block 12, as mentioned above. It is preferableto adjust the shape of the base block 12 and the cut length of thefitting notch 17 so that a center line (a straight line passing throughthe center of the widthwise direction of the bus bar 11) of the bus bar11 and a center line (a straight line passing through the center of thewidthwise direction of the top surface of the base block 12) of the baseblock 12 are in agreement when the base block 12 is viewed from the top.FIG. 4 shows that the center line of the bus bar 11 and the center lineof the base block 12 are in agreement with a center line B. By makingwidthwise (Y direction) dimensions of the base block 12 and the terminalblock 13 which is placed on the base block 12 to become equal, thecenter of the widthwise direction (Y direction) of the electromagneticshielding frame member 14 which covers the base block 12 and theterminal block 13 corresponds with each of the center lines.

The electromagnetic shielding frame member 14 prevents the propagationof electromagnetic waves to the inside of the IC receiving recess 21,and inside the electromagnetic shielding frame member 14 when the busbar 11 is installed to the electromagnetic shielding frame member 14,the strength of the magnetic field generated from the bus bar 11 isdistributed symmetrically to a plane A. As shown in FIG. 4, the plane Ais a plane which intersects perpendicularly in the length direction (Xdirection) of the electromagnetic shielding frame member 14, and is aplane which is located in the center of both ends of the lengthdirection of the electromagnetic shielding frame member 14. In thisembodiment, in order to cause the strength of the magnetic fieldgenerated from the bus bar 11 to be distributed symmetrically to theplane A inside the electromagnetic shielding frame member 14, by causingthe shape of the electromagnetic shielding frame member 14 to be arectangular parallelepiped and setting the plane A which divides therectangular parallelepiped into two rectangular parallelepipeds of thesame shape, the distribution of the magnetic field strength inside theelectromagnetic shielding frame member 14 is symmetric. Then, in thecenter line B which passes the centers of the Hall ICs 15, 16 and isplaced at a height C in the Z direction from the bottom wall in theelectromagnetic shielding frame member 14, the distribution of magneticflux Bw which the bus bar 11 generates inside the electromagneticshielding frame member 14 is as shown in FIG. 6. In the distribution ofFIG. 6, the width indicates positions in the X direction with theposition of the plane A as 0 (since the length of the electromagneticshielding frame member 14 is 12 mm in the length direction, the maximumof X width is assumed as 6 mm and the minimum is assumed as −6 mm.), andthe vertical axis indicates strength Bw of the magnetic field. Insidethe electromagnetic shielding frame member 14, the magnetic fieldstrength is distributed to be the largest near the center 0 of theelectromagnetic shielding frame member 14 in the length direction (inFIG. 6, about 5 mT), and decrease as towards both ends of theelectromagnetic shielding frame member 14 in the length direction (inFIG. 6, about 1.4 mT). That is, the magnetic field strength isdistributed to decrease symmetrically from the plane A towards the bothends (each at a position 6 mm from the center 0 in the length directionin FIG. 6) of the electromagnetic shielding frame member 14 in thelength direction (X direction). The reason why such magnetic fieldstrength distribution in the electromagnetic shielding frame member 14appears, that is, why the magnetic field strength becomes the largestnear the center 0 in the length direction of the electromagneticshielding frame member 14, is because the magnetic field generated fromthe bus bar 11 is reflected at any parts of the inner wall surfaces ofthe electromagnetic shielding frame member 14 (the electromagneticshielding frame member 14 is provided in order to strictly prevent thepropagation of electric waves from the outside of the electromagneticshielding frame member 14 to the inside, and simultaneously, a functionthat the electric waves inside the electromagnetic shielding framemember 14 are not propagated outside is also realized.), and suchreflected magnetic field may be propagated to pass the parts near thecenter 0 in the length direction of the electromagnetic shielding framemember 14.

The shape of the electromagnetic shielding frame member 14 is notrestricted to a rectangular parallelepiped, but may be other shapes aslong as two spaces of the same shape are obtained when the plane whichintersects perpendicularly in the length direction of the bus bar 11divides the inside of the electromagnetic shielding frame member 14.When a dielectric material is enclosed inside the electromagneticshielding frame member 14, and the plane which intersectsperpendicularly in the length direction of the bus bar 11 divides thedielectric material inside the electromagnetic shielding frame member14, the distribution of the magnetic field strength inside the twospaces may become symmetrical. In short, the magnetic field strengthgenerated from the current path only has to become symmetricallydistributed to the plane A which intersects perpendicularly in thelength direction of the bus bar 11.

The front and back parts of the two Hall ICs 15, 16 in the bus barlongitudinal direction, as shown in FIG. 4, are arranged to be symmetricto the plane A. These Hall ICs 15, 16 are located at different heights(Z direction) C and D in the electromagnetic shielding frame member 14,as shown in FIG. 5. Here, the two Hall ICs 15, 16 are described to bearranged in positions along the center line B, respectively. Thus, sincethe Hall ICs 15, 16 are arranged in the positions where the magneticfield strength generated from the bus bar 11 becomes the largest easily,an effect is achieved that the size of a current which flows through thebus bar 11 can be measured with sufficient precision.

Therefore, since the front and back parts of the two Hall ICs 15, 16 inthe bus bar longitudinal direction are arranged to be symmetric to theplane A as mentioned above, and the two Hall ICs 15, 16 are located atthe different heights (Z direction) C and D in the electromagneticshielding frame member 14, the two Hall ICs 15, 16 are exposed at placeswhere the magnetic field strength is different. Therefore, thesensitivities of the two Hall ICs 15, 16 are adjusted so that currentvalues outputted according to the detected magnetic fields are identicalto each other in a normal state, as described later. That is, the HallICs 15, 16 of different characteristics are used. Therefore, each of theHall ICs 15, 16 will output a current value in an identical level in thenormal state.

On the other hand, when the output current values of the Hall ICs 15, 16arranged as mentioned above differ, it can be determined that either ofthe Hall ICs 15, 16 fails. FIG. 8 is a failure detecting circuit of theHall ICs 15, 16. In the failure detecting circuit, an electric currentcomparator 31 compares the output currents of the Hall ICs 15, 16. Basedon this comparison result, a failure determination circuit 32 determineswhether either of the Hall ICs 15, 16 fails or both of the Hall ICs 15,16 are normal, and the determined result is displayed on an indicator33.

The Hall ICs 15, 16 are arranged to pass the center line B in thewidthwise direction of the bus bar 11, and the right and left parts ofthe Hall ICs 15, 16 in the bus bar widthwise direction become symmetricto a plane A′ shown in the FIG. 5 which intersects perpendicularly withthe bus bar 11.

The electromagnetic shielding frame member 14 prevents the propagationof electromagnetic waves to the inside of the IC receiving recess 21,and inside the electromagnetic shielding frame member 14 when the busbar 11 is installed to the electromagnetic shielding frame member 14,the strength of the magnetic field generated from the bus bar 11 isdistributed symmetrically to the plane A′. As shown in FIG. 5, the planeA′ is a plane which passes the center line B (refer to FIG. 4) in thewidthwise direction of the bus bar 11 which is extended in the lengthdirection (X direction) of the electromagnetic shielding frame member14, and intersects perpendicularly with the bus bar 11. In order tocause the strength of the magnetic field generated from the bus bar 11to be distributed symmetrically to the plane A inside theelectromagnetic shielding frame member 14, by causing the shape of theelectromagnetic shielding frame member 14 to be a rectangularparallelepiped and setting the plane A′ which divides the rectangularparallelepiped into two rectangular parallelepipeds of the same shape,the distribution of the magnetic field strength inside theelectromagnetic shielding frame member 14 is symmetric. Then, in thewidthwise direction (Y direction) which passes the centers of the HallICs 15, 16 and is positioned at a height C in the Z direction from thebottom wall in the electromagnetic shielding frame member 14, thedistribution of magnetic flux Bl which the bus bar 11 generates insidethe electromagnetic shielding frame member 14 is as shown in FIG. 7. Inthe distribution of FIG. 7, the width indicates positions in the Ydirection with the position of the plane A′ as 0, and the vertical axisindicates strength Bl of the magnetic field. Inside the electromagneticshielding frame member 14, the magnetic field strength is distributed tobe the smallest near the center 0 of the bus bar 11 in the widthwisedirection, and increase as towards both ends of the bus bar 11 in thewidthwise direction. That is, the magnetic field strength is distributedto increase symmetrically from the plane A′ towards the both ends of thebus bar 11 in the widthwise direction (Y direction). The reason why suchmagnetic field strength distribution in the electromagnetic shieldingframe member 14 appears is because the cross-section of the bus bar 11is symmetric in the widthwise direction.

Therefore, since the left and right parts of the two Hall ICs 15, 16 inthe bus bar widthwise direction are arranged to be symmetric to theplane A′, and the two Hall ICs 15, 16 are located at the differentheights (Z direction) C and D in the electromagnetic shielding framemember 14 as mentioned above, the two Hall ICs 15, 16 are exposed atplaces where the magnetic field strength is different. Therefore, thesensitivities of the two Hall ICs 15, 16 are adjusted so that currentvalues outputted according to the detected magnetic field are identicalto each other in a normal state, as described above. Therefore, each ofthe Hall ICs 15, 16 will output a current value in an identical level.On the other hand, when the output current values of the Hall ICs 15, 16arranged as mentioned above differ, it can be determined that either ofthe Hall ICs 15, 16 fails.

The Hall ICs 15, 16 are arranged (separately) along the Z axialdirection which is a height direction, and directed to the center (A′)in the Y direction which is the bus bar widthwise direction and thecenter (A) in the X direction which is the bus bar longitudinaldirection. When it is assumed that a current of 100 A flows in the busbar 11, the magnetic flux density B₁₀₀ which is generated in the Ydirection in the width direction center of the bus bar 11 by the currentwhich flows ino the bus bar 11 is like, for example, a graph shown inFIG. 9. That is, if the distance L from the surface of the bus bar 11becomes longer, the magnetic flux density B₁₀₀ will become smaller. Forexample, the magnetic flux density B₁₀₀ of the Hall IC 16 at the Cposition shown in FIG. 5 is 0.07 mT/A, and the magnetic flux density ofthe Hall IC 15 at the D position is 0.059 mT/A. Thus, since the magneticflux densities generated at the positions C and D differ from eachother, the sensitivities of the Hall ICs 15, 16 are adjusted in order toobtain the same output.

FIG. 10 shows current detection ranges for which a voltage output of1.5V at the maximum current is possible when two Hall ICs 15, 16 whosesensitivities can be adjusted in a range of 0.05 to 0.3 V/mT are used.These current detection ranges can be obtained with calculation from themagnetic flux density B₁₀₀ (refer to FIG. 9) at the C and D positionsand the sensitivities S of a Hall ICA and a Hall ICB. It can be seenfrom the graph of FIG. 10 that when the current outputs I of the twoHall ICA and Hall ICB are the same, the overlapped range (85 to 428 A)becomes a failure detectable range. It is possible to measure a widercurrent range if individual sensitivities are corresponded. That is, asshown in FIG. 10, by changing the outputs of the two Hall ICA and HallICB, a wide range current measurement becomes possible. When the twoHall ICA and Hall ICB whose sensitivities can be adjusted in the rangeof 0.05 to 0.3 V/mT are used, the failure detectable range is 85 to 428A, and the wide current measurement range is 72 to 508 A.

As described above, according to this embodiment, it is not necessary toinclude the core in structure like before. It is not necessary toarrange two Hall ICs in parallel to make it possible to compare sensoroutputs and determine the failure of a current sensor like a related-artexample. Therefore, one magnetic detector is arranged on the same plane,and the simplification and downsizing of a current detection apparatuscan be realized.

By changing the sensitivities of the Hall ICs 15, 16, the same outputsare obtained, and by comparing outputs, failure diagnosis can beperformed. Thereby, failure determination of a magnetic detector (Hallelement) can be performed easily without being affected by an externalmagnetic field.

If individual sensitivities are set for the Hall ICs 15, 16, a widecurrent range can be detected with sufficient precision withoutincreasing the size.

Although it is described in this embodiment that a magnetic field whicha current flowing in the bus bar 11 generates is detected, a currentwhich flows in current paths other than a bus bar, for example, a usualelectric wire, can be detected by using the above-mentionedelectromagnetic shielding frame member and the Hall ICs, and failuredetection of the Hall elements also can be performed like above.

Although the present invention is described in detail with reference tothe embodiments, it is apparent that various modifications andamendments may be made by those skilled in the art without departingfrom the spirit and scope of the invention.

REFERENCE SIGNS LIST

-   -   11: bus bar (current path)    -   14: electromagnetic shielding frame member    -   15, 16: Hall IC (magnetic detector)    -   23: insulative board (board)    -   23 a, 23 b: front and back surface    -   32: failure determination circuit (control circuit)

What is claimed is:
 1. A current detection apparatus, comprising: twomagnetic detectors that are arranged oppositely on a front surface and aback surface of a board which is located above a current path in orderto detect a strength of a magnetic field which is generated by a currentwhich flows in the current path, wherein sensitivities of the twomagnetic detectors are adjusted so that values outputted from the twomagnetic detectors depending on detected magnetic fields are identicalto each other in a normal state; an electromagnetic shielding framemember that is mounted on the current path so that the two magneticdetectors and a part of the current path where the two magneticdetectors are arranged are accommodated inside the electromagneticshielding frame member; and a control circuit that determines whether afailure occurs in either of the two magnetic detectors from a differencebetween magnetic fields detected by the two magnetic detectors,respectively in a failure detectable range in which both of the twomagnetic detectors detect the magnetic fields, and measures the strengthof the magnetic field based on the value outputted from one of the twomagnetic detectors in a wide current measurement range in which said oneof the two magnetic detectors detects the magnetic field.